Science Breakthrough: Plate Armor is Heavy

Researchers in the U.K. have discovered that 15th century knights who wore heavy suits of armor into battle got tired a lot faster than soldiers who went unarmored.

There was a time, back before the invention of the Uzi and the atom bomb, when the King's finest soldiers rode into battle dressed in gleaming, head-to-toe armor that protected them from the slings, arrows and pithy insults of their lower-class adversaries. Armored knights were literally the tanks of the medieval battlefield. But modern tanks aren't without their weaknesses and neither were their centuries-old counterparts. Those armor-plated duds were seriously heavy, weighing in at anywhere from 60 to 110 pounds, which lead researcher Dr. Graham Askew of the University of Leeds described as "a huge fraction of the wearer's body weight."

Enter science! Four volunteers who take part in reenactments for the Royal Armories at Leeds were suited up in "exact replica" armor from England, Gothic Germany and Italy, and then put onto a treadmill. Researchers measuring their oxygen intake, carbon dioxide production and the precise movement of their limbs found that walking and running while wearing armor required double the normal amount of energy, while the heavy breast and back plates made things even worse by preventing wearers from taking long, deep breaths.

And it's not just the raw weight that's problematic, but also how it was carried in the field. Modern soldiers carry comparable loads in backpacks, yet have far greater mobility and endurance. "We found there was a big difference: it is much more 'expensive' to carry the load as a suit of armor than it is to carry the load in a backpack," Askew said.

"We were interested to find out why that was - and one of the main reasons is that if you wear a suit of armor, a lot of the weight is carried on the legs - about 7 to 8 kilograms [15 to 17 pounds] of it," he explained. "And this means when you walk and you swing your legs, you are requiring a lot more muscular effort, and that costs you a lot more energy."

The French learned this the hard way at the Battle of Agincourt in 1415, when their numerically superior force was overwhelmed and slaughtered by an invading English army after an exhausting slog through about 300 meters of mud. And while it may seem silly to "confirm" that knowledge 600 years later - "plate armor is heavy" isn't exactly the most revolutionary breakthrough ever - this is the first time that anyone's ever gone at it scientifically.

"It is interesting to use scientific method to answer these questions, and it confirms what we have always suspected - heavy armor would very much reduce your ability to run around," said Thom Richardson, keeper of armors at the Royal Armories at Leeds. But despite the obvious downsides, its value in battle was very real, he added. "No-one wears stuff on the battlefield if it isn't useful."